The long-range objective of this project is to clarify the genetic and biochemical substructure of the hexosaminidase deficiency diseases, a group of recessively inherited lysosomal storage diseases. Using a coordinated clinical, genetic, and biochemical program we are trying to determine a) How many subunits (or distinct genetic loci) are required for the hexosaminidase enzyme? b) Which enzyme subunit is the site of the mutational alteration in the various hexosaminidase deficiency diseases due to structural gene mutations? and c) How does the mutational alteration of an enzyme subunit affect the enzyme protein to reduce its activity? At least 12 hexosaminidase deficiency diseases are known, 3 of which were discovered in our laboratory. We are studying 4 of these in patients and carriers using a variety of techniques including 1) fractionation of fibroblast or urinary hexosaminidases by isoelectricfocussing; 2) studying the abnormal residual hexosaminidases for abnormal kinetic properties, abnormal lability of the enzymes or other abnormal properties suggesting a mutation affecting the active site, subunit binding, or other enzyme protein function; 3) somatic cell hybridization with Tay-Sachs or Sandhoff fibroblasts to see if genetic complementation occurs; and 4) natural substrate studies. Our preliminary evidence suggests that three of these disorders may be beta-subunit disorders and one an alpha-subunit disorder. One disorder appears to be the result of defective subunit binding. Abnormally heat-labile hexosaminidases has been found in two disorders. We propose to extend these studies to all our new hexosaminidase disorders and ultimately to all hexosaminidase deficiency diseases. In this way it may be possible to incorporate these disorders into a multiple loci-multiple alleles system as has been done with the hemoglobinopathies. And it may be possible to show for each disorder how the mutation causes a reduction in enzyme activity.